Alladi Ramakrishnan Hall

Superconductivity at extremely low carrier density: Bismuth

Srinivasan Ramakrishnan

TIFR, Mumbai

Bismuth(Bi) has played a very important role in uncovering many interesting physical properties in condensed matter research and continues to draw enormous scientific interests due to its anomalous electronic properties. Unlike metals where there is roughly one mobile electron per atom, in a semi-metal like Bi, the concentration of mobile electrons is extremely low (100,000 atoms share a single mobile electron). Hence, the superconductivity (SC) in bulk Bi is thought to be very unlikely at a currently achievable temperature (~40 μK). In this talk, I will describe the first-ever observation of bulk SC in Bi single crystals (99.9999% pure) below 530 μK under ambient pressure with an estimated critical magnetic field of 5.2 μT (one fifth of earth’s magnetic field) at absolute zero1. The standard models (superconductivity) cannot explain this phenomenon because the characteristic thermal energy is comparable to the Fermi energy in Bi and a new theory is necessary.

1. Om Prakash, Anil Kumar, A. Thamizhavel and S. Ramakrishnan, Science (2016, under review).